1. Field of the Invention
The present invention relates to an automotive traction control system applied for suppressing acceleration-slip occurring at driven wheels during quick depressing operation of the accelerator pedal, such as quick starting, quick acceleration, or the like, and specifically to a system being capable of suppressing acceleration-slip through a traction brake control according to which excessive driving force exerted on the driven wheels is suppressed via a brake fluid pressure generated by an external brake fluid pressure source and/or through a traction throttle control according to which the excessive driving force is suppressed by changing a throttle opening angle and a throttle opening and closing speed.
2. Description of the Prior Disclosure
Recently, there have been disclosed and developed various automotive traction control systems, in which the increase, holding, or decreasing in a wheel-cylinder pressure can be independently carried out in left and right driven wheels during acceleration slip, by means of an external brake fluid pressure source generating a brake fluid pressure irrespective of depression of the brake pedal. One such conventional traction control system had been disclosed in Japanese First Publication Tokkai Showa 63-31859. The conventional traction control system teaches a variable target slippage control for a driven wheel depending upon a vehicle running condition, such as a straight-ahead driving or cornering. In the embodiment of the Japanese First Publication Tokkai Showa 63-31859, the control unit variably controls the target slip value for the driven wheel, such that the target slip value utilized during straight-ahead driving is set at a higher value than that utilized during cornering, so as to assure a sufficient driving force during straight-ahead driving and to provide a high cornering stability. The conventional traction control system tends to easily transit to an acceleration slip control during cornering. In contrast to the above, the conventional traction control system tends not to easily transit to the acceleration slip control during straight-ahead driving. Therefore, the conventional traction control system has some drawbacks as herebelow described in detail.
In case that the target slip value for the driven wheel has been properly tuned at a low level depending on change in the vehicle running condition from the straight-ahead driving state to the cornering state, a target slip value recovery is retarded when the vehicle running condition returns again from the cornering state to the straight-ahead driving state, since a low tuned target slip value is maintained until the running condition completely transits to the straight-ahead driving state.
In case that the target slip value for the driven wheel has been properly tuned at a high level depending on change in the vehicle running condition from the cornering state to the straight-ahead driving state, a cornering stability is reduced when the vehicle running condition returns again from the straight-ahead driving to the cornering state, since a high tuned target slip value is maintained within a transient state shifting from the straight-ahead driving state to the cornering state.